1. Field of the Invention
The invention relates to a battery module in which a plurality of battery cell packs are stacked.
2. Description of Related Art
A battery module in which a plurality of battery cell packs are stacked is, for example, described in Japanese Patent Application Publication No. 2003-133188 (JP 2003-133188 A) and Japanese Patent Application Publication No. 2006-196230 (JP 2006-196230 A).
JP 2003-133188 A describes a structure that a heat conductor is arranged between any adjacent cells and heat emitted from the cells is dissipated from both end portions of each heat conductor to cooling elements. In addition, JP 2006-196230 A describes a structure that an interlayer member that serves as a heat radiating member is arranged between any adjacent battery cells and heat emitted from the battery cells is radiated from both end portions of each interlayer member.
The configuration of a battery module 100A according to the related art is described with reference to FIG. 10 to FIG. 12. FIG. 10 is a cross-sectional view that shows the structure of the battery module 100A and that is taken along the line X in FIG. 11. In addition, FIG. 11 is a perspective view that shows the structure of each battery cell pack 150 and the structure of each heat dissipation plate 110. FIG. 12 is a cross-sectional view that shows a cooling structure employed in the battery module 100A.
As shown in FIG. 10, the heat dissipation plate 110 is arranged between any adjacent two of the plurality of battery cell packs 150. Each heat dissipation plate 110 absorbs heat emitted from the battery cell packs 150 and then radiates the heat to the outside. Thus, the battery cell packs 150 and the heat dissipation plates 110 are alternately arranged. For example, in the single battery module 100A, ninety battery cell packs 150 are stacked in a stacking direction S.
Each battery cell pack 150 generally has a structure as follows. Lithium cobaltate (LiCoO2) or lithium manganate (LiMnO2) is used as a positive electrode, and graphite (carbon) is used as a negative electrode. A separator is interposed between the electrodes for electrical insulation. Several layers of the electrode plates are stacked and then sealed with aluminum lamination, or the like, together with an electrolytic solution.
Pressing plates 101 are arranged on both end portions of the battery cell packs 150 and heat dissipation plates 110 in the stacking direction S. The battery cell packs 150 and the heat dissipation plates 110 are alternately stacked in the stacking direction S. Heat emitted from the battery cell packs 150 located at both ends is absorbed by the pressing plates 101 and then radiated from the pressing plates 101. The pressing plates 101 are made of a material having an excellent thermal conductivity (aluminum, or the like).
As shown in FIG. 11, each battery cell pack 150 has a flattened body portion and electrode portions 150a that are provided on the upper end portion of the body portion. The plurality of battery cell packs 150 are electrically connected in series with one another.
Each heat dissipation plate 110 has an interlayer plate portion 110a and side wall plate portions 110b, and has a C shape as a whole. The interlayer plate portion 110a is in plane contact with the body portion of the battery cell pack 150, and is interposed between the adjacent battery cell packs 150. The side wall plate portions 110b extend in the stacking direction with respect to the interlayer plate portion 110a on both ends of the interlayer plate portion 110a. 
As shown in FIG. 12, for the stacked battery cell packs 150 and heat dissipation plates 110, coolers 130 are respectively arranged on the outer faces of the side wall plate portions 110b of the heat dissipation plates 110 along the battery module 100A. The coolers 130 are arranged along both side faces of the battery module 100A. Each cooler 130 has a cooling pipe 131 and a cooling medium 132. The cooling pipe 131 is in contact with the outer faces of the side wall plate portions 110b. The cooling medium 132 is introduced into the cooling pipe 131.
Grease 140 is applied between the cooling pipes 131 and the outer faces of the side wall plate portions 110b in order to increase heat transfer therebetween.
Heat emitted from the battery cell packs 150 conducts through the heat dissipation plates 110 and is absorbed by the cooling pipes 131. By so doing, an increase in the temperature of the battery cell packs 150 is suppressed to thereby maintain the performance of the battery cell packs 150 and extend the service life of the battery cell packs 150.
As shown in FIG. 12, heat emitted from each battery cell pack 150 roughly includes flow of heat that is shown arrow B in the drawing and flow of heat the is shown arrow A in the drawing. The flow of heat (arrow B in the drawing) reaches any one of the side wall plate portions 110b through the interlayer plate portion 110a of the heat dissipation plate 110. The flow of heat (arrow A in the drawing) reaches the interlayer plate portion 110a and the side wall plate portion 110b through the battery cell pack 150.
In this case, heat concentrates at portion Y (circled in FIG. 12) of the interlayer plate portion 110a, which is in proximity to the side wall plate portion 110b. Thus, the thermal resistance increases and, as a result, heat is hard to conduct to the side wall plate portion 110b. Therefore, there occurs nonuniform temperature distribution in the battery cell pack 150. This may lead to a decrease in the performance of the battery cell pack 150.
It is conceivable that the thickness of each heat dissipation plate 110 is increased in order to decrease the thermal resistance. However, if the thickness of each heat dissipation plate 110 is increased, this leads to an increase in the weight of the battery module and an increase in the size of the battery module.